Fortrat J O, Sigaudo D, Hughson R L, Maillet A, Yamamoto Y, Gharib C
Faculté de Médecine Grange-Blanche, Laboratoire de Physiologie de l'Environnement, 8, Avenue Rockefeller, 69373 Lyon, France.
Auton Neurosci. 2001 Jan 14;86(3):192-201. doi: 10.1016/S1566-0702(00)00212-5.
We postulated that a change in complex dynamics of the cardiovascular system could be involved in the orthostatic intolerance observed after simulated weightlessness. Supine recordings of 1024 consecutive pulse intervals and systolic blood pressures were obtained on 7 subjects adapted to a 42 day head-down bed rest (day 22 and 42) but also before and 6 days after head-down bed rest (-6 degrees). Coarse graining spectral analysis was used to extract the non-harmonic (fractal) component from each time series. The power spectral densities of this fractal component are inversely proportional to their frequency (1/f beta). We fitted an inverse power law estimate to the fractal component to determine the spectral exponent beta. The complex dynamics of blood pressure and heart rate variability were also analyzed by correlation dimension and non-linear prediction. Bed rest induced orthostatic intolerance in 4 subjects. There was a significant increase in the spectral exponent beta of RR-interval variability during and after head-down bed rest (before: 1.039 +/- 0.090; during: 1.552 +/- 0.080 and 1.547 +/- 0.100; after: 1.428 +/- 0.040). Analysis of the blood pressure dynamics indicated lower correlation dimensions during head-down bed rest and higher coefficients of predictability after head-down bed rest. Complexity alterations of RR-interval and blood pressure variability were not linked with one another during head-down bed rest. These alterations seemed to be correlated with the orthostatic intolerance observed after bed rest. These results suggest a change of the integration level of cardiovascular autonomic regulation.
我们推测，心血管系统复杂动力学的变化可能与模拟失重后出现的体位性不耐受有关。对7名适应42天头低位卧床休息的受试者（第22天和第42天），以及头低位卧床休息前和后6天（-6度），连续记录1024个仰卧位脉搏间期和收缩压。采用粗粒化频谱分析从每个时间序列中提取非谐波（分形）成分。该分形成分的功率谱密度与其频率成反比（1/fβ）。我们对分形成分拟合了反幂律估计值，以确定频谱指数β。还通过关联维数和非线性预测分析了血压和心率变异性的复杂动力学。卧床休息导致4名受试者出现体位性不耐受。头低位卧床休息期间及之后，RR间期变异性的频谱指数β显著增加（之前：1.039±0.090；期间：1.552±0.080和1.547±0.100；之后：1.428±0.040）。血压动力学分析表明，头低位卧床休息期间关联维数较低，头低位卧床休息后可预测性系数较高。头低位卧床休息期间，RR间期和血压变异性的复杂性改变彼此不相关。这些改变似乎与卧床休息后观察到的体位性不耐受有关。这些结果提示心血管自主神经调节的整合水平发生了变化。
